Antique post-and-beam renovation: insulation questions!

10 years ago

Hi folks, I am helping my mom with a major whole-house renovation of an 1800's post-and-beam cape in Maine. The home has been gutted and an absurd amount of structural work had to be done... basically building a new house inside the shell of the old one! She and I have just finished running all the electrical wiring in the gutted walls, and the next step is insulation and drywall.

She has decided to go with blown-in cellulose in the exterior walls and second floor ceiling (which is the roof... so basically a cathedral ceiling.) Unfortunately the exterior walls are pretty thin, in some places the cavity is only 3.5" deep, in others it may be 4.5". I had hoped she could get a really high R-value foam, but it was too costly. Please keep in mind that this is a very low-budget reno. She is getting spray foam on the basement/sill walls, though.

My question has to do with all the holes and gaps in the original sheathing. It's just wide planks, of course, and there are numerous knotholes and gaps up to 2" wide throughout the house. In some areas, the wood clapboard siding had to be removed, and there is Typar building paper in those areas, but I can see a whole lot of daylight through those walls! And in other areas the original clapboards (with their very old tarpaper beneath) remain, so there isn't even new building paper in those areas.

I am wondering whether these gaps and holes are going to further degrade her already light R-value. If I read the web sites right, the recommended R-vales for our climate are R13-21 for the cavity and R5-6 for the sheathing. Her cellulose in the cavity will be just R12 in the 3.5" areas, so I'm worried that these gaps in the old sheathing will further lower the recommended R5-6 sheathing value.

Removing all of the clapboards and re-sheathing the house is NOT a possibility. I'm wondering if there is anything we can do now, while the walls are open and before the insulation is installed, to increase the R-value of these walls from the inside. Spray foam each and every crack/gap with Great Stuff? Install some inexpensive type of barrier before the cellulose goes in?

Any suggestions?

Thank you!

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Comments (7)

jmc01
10 years ago
I'd post this on wavyglass dot org....to the old home forums there.
PRO
Joseph Corlett, LLC
10 years ago
I'd rethink the cellulose. If it gets wet from all that "daylight" showing, your R value will suffer and you'll have mush in your walls. I doubt the foam will have this problem.
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Stacey Collins
Original Author
10 years ago
I don't think there is any option about the cellulose due to budget. (It is not my decision.) But I AM trying to help advise on how to make it work best... so maybe sealing all those cracks and holes from the inside now is what we need to do? How and with what?
User
10 years ago
Shop more carefully for closed cell spray foam. Since it solves all of your problems, it might be the only effective solution.

When I have renovated post & beam houses I furred the interior walls and incorporated the P&B structure in the wall cavity for 5 1/2" of insulation.

Your options are to pay now or pay later so compare the correct numbers over a reasonable time period. Look for tax breaks and gas company rebates. Talk to local builders and architects.
Stacey Collins
Original Author
10 years ago
Thanks Renovator8, furring out interior walls would be good advice for someone early in the reno process. Unfortunately we are well past that now. Walls are completely furred already and ready for sheetrock. The budget is to-the-dollar tight and I know my mom would not consider undoing all that work and re-furring the walls. She was told early on that there would be "plenty" of space for insulation as it is, and went with that.
A very knowledgeable insulation team originally told her the cellulose would be fine (they also do spray foam, so it was not a selling issue) but I don't think they knew about all the gaps/cracks at that time, because the walls were closed up then. I've recommended she discuss this with them, of course, but wanted to see if other people had encountered this same issue and what they'd used to fill the holes.
insteng
10 years ago
You definitely want to try and seal up as many cracks and gaps as possible. My farm house was built in 37 and as I redo the exterior walls I have been sealing up any gaps I see with the spray in foam and then stapling a heavy plastic to further block any air coming in. I also sealed up any holes where wiring was run through the studs. It helped stop a lot of air leaks that way.Then I have just put in the regular R-13 insulation. Though it doesn't get near as cold here it really made a big difference on the temperature. It is a lot cooler in the summer and warmer in the winter.
worthy
10 years ago
I don't think there is any option about the cellulose due to budget.

Your Mom's budget will take a bigger hit curing the effects of permanently wet cellulose.

Antique post-and-beam renovation: insulation questions!

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jmc01

Joseph Corlett, LLC

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Antique post-and-beam renovation: insulation questions!

Comments (7)

jmc01

Joseph Corlett, LLC

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Stacey CollinsOriginal Author

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insteng

worthy

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